Private Sub Button33_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button33.Click
Dim rowindex As String
Dim found as Boolean = false
For Each row As DataGridViewRow In DataGridView1.Rows
If row.Cells.Item("ITEM_ID").Value = TextBox5.Text Then
rowindex = row.Index.ToString()
found = true
Dim actie As String = row.Cells("PRICE").Value.ToString()
MsgBox(actie)
Exit for
End If
Next
If Not found Then
MsgBox("Item not found")
End if
End Sub

What this does is that it loops through all the items. When it finds a match it sets found to true. If not item is found then "found" is false when the loop ends. And if "found" is false then you display "Item not found". Hope you understand, otherwise ask :)